Heat exchanger

ABSTRACT

A heat exchanger, especially a condensate-evaporator or like unit for a gas-rectification column in which a prismatic heatexchange body is surrounded by a cylindrical housing such that sectoral compartments form passages for the fluids traversing the heat exchanger body. The body of the heat exchanger consists of a stack of plate pairs, the plates of each pair being corrugated such that alignment of the corrugations produces tubes. The tubes of the stacked arrays are staggered from one array to the next and communicate via a space at the bottom of the cylinder housing, with one of the sectoral compartments. The device functionally connects but physically separates the high-pressure and low-pressure sides of a column.

Nasser et a1.

atet

[ 1 5 HEAT EXCHANGER 1,316,636 9/1919 Opitz ..l/l70 inventors: Gama El Din Nasser, gg; Hans gmith ..l65/l66 olmck ..165/170 waldmann, wmfratshauser' both of 3,256,704 6/1966 Becker.... ..62/42 Germany 3,397,547 8/1968 Erb ..62/29 [73] Assignee: Linde Aktiengesellschatt,

wiesbaden, Germany Primary Examzrten-Norman Yudkoff Assistant ExammerArthur F. Purcell Filed: June 15, 1970 Att0rneyl(arl F. Ross [21] Appl. No.: 45,976

[57] ABSTRACT [30] Foreign Application Priority Data A heat exchanger, especially a condensate-evaporator or like umt for a gas-rectification column in which a June 14, Germany prismajc heat exchange is surrounded a cylindrical housing such that sectoral compartments UuS- CL l form passages for the fluids traversing the heat [5 Il'rt. Cl. ex hanger The of the heat exchanger con- Field of Search 29, sists of a stack of plate pairs, the plates of each pair 42 being corrugated such that alignment of the corrugations produces tubes. The tubes of the stacked arrays References Cled are staggered from one array to the next and commu- UNITED STATES PATENTS rucate yia a space at the bottom of the cylinder housmg, with one of the sectoral compartments. The 3,610,330 10/1971 Nasser ..165/166 device functionally connects but physically separates 2,044,372 6/1936 Twomey... the high-pressure and low-pressure sides of a column. 3,106,957 10/1963 Cann0n.... 2,017,240 10/1935 Frank] ..62/39 14 Claims, 7 Drawing Figures 30 22 2| I 1 m t 1 x I I ls; l 36 ,1 s i 17 ,1 m, 1. I l l 1 7 6 3| I 34 14b I I 9 1 PATENIEDHARl 3197s I 3,720,071

SHEET 10F 3 I o 2 INVENTORS Gama! el din Nasser BY Hons Woldmonn FIG] 5M9? ATTORNEY PATENTEUHARI 3197s SHEET 2 BF 3 Fuss ATTORNEY PATENTEUMARI 3 I975 SHEET 3 BF 3 III II F I G 5 F l G 6 NIHIH||| HHHHHI UHHHH l l W W INVENTORS;

Gomol el din Nasser Hons Woldmonn 33ml 9 TM ATTORNEY HEAT EXCHANGER CROSS-REFERENCE TO COPENDING APPLICATION The present invention relates to a heat exchanger of the general type described and claimed in our commonly assigned copending application Ser. No. 773,082, filed Nov. 4, 1968 (now U.S. Pat. No. 3,610,330 issued Oct. 5, 1971) by Gamal el din Nasser, one of the present joint inventors.

FIELD OF INVENTION Our present invention relates to heat exchangers and, more particularly, to devices for the indirect heat exchange between fluids, i.e. heat transfer through a thermally conductive wall separating two compartments traversed by the respective fluids; in specific terms, heat exchangers of this type may be used for gas rectification, i.e. the separation of gas mixtures by lowtemperature processes such as condensation and refluxing, and especially air rectification in accordance with the principles of the Linde-Frankl method.

BACKGROUND OF THE INVENTION In the above-mentioned application Ser. No. 773,082, it has been observed that earlier heatexchange systems for the cooling of hot-gas streams make use of a tube bundle consisting of a multiplicity of generally rectilinear or straight tubes held in place by a pair of tube sheets at the ends of the tube bundle. A cooling fluid, which may be of a higher pressure, flows between the tubes of the bundle, i.e. traverses the interstices of the tube bundle. It has also been pointed out that such tube bundles and the associated sheets are difficult to manufacture, expensive and require reinforcements to enable the tube sheets to withstand the stresses generated by the elevated-pressure cooling medium.

In addition, tube-bundle heat exchangers having tube sheets at the gas-entry side of the device have the substantial disadvantage that a relatively large temperature differential exists across the tube sheet since the latter, at one side, is exposed to the high-temperature gas and at the other side is exposed to the low-temperature and high-pressure cooling medium.

Additionally, the tube sheet is subjected to a substantial pressure differential equal to the difference between the hot-gas pressure on the entry side and the coolant pressure on the opposite side of the tube sheet. In such earlier systems, it was found necessary to accommodate the thermal and pressure stresses by the use of relatively thin-walled tube sheets with reinforcing webs or rods, in a lattice configuration, forming a stiffening means. This arrangement was both expensive and unsatisfactory, since the cooling efficiency was relatively low; use of the system was also characterized by overheating and accelerated corrosion at the heatexchange walls. Corrosion was especially a problem when a condensable or condensate-containing medium was employed.

Attempts to avoid this disadvantage by passing the high-temperature gas through the chamber surrounding the tube bundle and passing the cooling medium through the tubes thereof, were not satisfactory either. Finally, the earlier systems gave rise to high-pressure drops in the tube bundle, low heat-exchange efficiency and high-pressure drops in the heat exchange medium as well.

In the improved system of the aforementioned application, however, these disadvantages were obviated by providing a tube-bundle heat exchanger with a pair of tube plates lying in planes parallel to the array of mutually parallel tubes to be formed therebetween and having on their confronting sides a plurality of spacedapart parallel concavities or corrugations which mutually register to constitute the respective tubes between them. The relatively thin-walled plates were preferably formed with the respective concavities by deformation of the plates to yield corrugations. Each concavity extended over an arc of about and the concavities were separated by webs lying in a diametral plane of the tubes of the array and generally planar so as to be coextensive with the corresponding webs of the confronting plate. The webs form reinforcing ribs between each pair of tubes of the particular array. Consequently, it can be said that each tube of the heat exchanger of application Ser. No. 773,082 is defined between a pair of such plates which are in approximate mirror-symmetry about a plane of symmetry extending through the axes of all of the tubes of a particular planar array and defined by the abutting faces of the flat rectangular webs between each pair of tubes of the array.

The tubular members themselves were constituted by semicylindrical corrugation troughs which registered with corresponding troughs of the oppositely facing plate. The plates were generally rectangular in plan view but were formed at their small sides or ends with outwardly flared or bent quarter-round flanges or lips (marginal portions) which were welded to the outwardly turned corresponding flanges of neighboring plates so that the interconnected flanges together formed end walls or bottoms of the chambers between the tubes constituted by the pairs of mutually facing registering corrugations in a construction generally similar to that of a unitary tube sheet. Furthermore, the longitudinal edges of the plates of each array were welded together parallel to the corrugations and the tubes constituted thereby. The tubes of each array defined between each pair of such plates were offset or staggered with respect to the neighboring tubes, approximately by the diameter of the tubes and in a direction perpendicular to the tubes. If each pair of plates was formed with an array of semicylindrical corrugations in accordance with the principles of application Ser. No. 773,082, the plates could constitute unit elements which were reversed with respect to one another but were of identical form. The plates could then be welded together in mirror symmetry. A stack of similar plates was joined together to form the tube bundle, the plates being mass-produced at relatively low cost.

Each of the plates was of a length slightly more than twice the length of the array and was bent at the end of the rectangle to form a pair of plate portions whose corrugations opened in opposite directions so that when the corrugated portions of the plate on either side of the bend overlay or confronted one another, the corrugations of one plate portion constituted right-hand tube halves while the corrugations of the other plate portion formed left-hand tube halves of the next array. The width of this double-length plate corresponded to the height of the tube array. At the bent ends at the opposite end of the array, i.e. remote from the bent zone, the rounded outwardly-curved flanges were provided, for contiguous welding to the adjoining sets of plate portions. Advantageously, the corrugations in the tube portions of the double-length plates were so formed as to be offset from one another by approximately half of a center-to-center distance between the pairs of semicylindrical corrugations.

The end edges of the borders of the plates are provided with transition members on flanges which could also be described as leveling flanges adapted to affix the tube bundle to the heat-exchanger housing. The latter was an elongated casing which surrounded the body of the tube bundle and was provided with radial inlet and outlet fittings to receive the cooling liquid and to remove any residual cooling liquid as well as vapors formed in the coolant compartment. The housing also comprises a pair of hood members in the form of angular flanges to which the leveling flanges of the plates were welded. The ends of the plates proximal to the flange rings were formed with corrugations or pleated portions designed to accommodate thermal expansion or contraction stresses at the hot-gas side of the tube bundle. The space between the tube arrays at each end of the tube bundle was defined between sets of covers and walls constituted by the quarter-circular outwardly flat edges of the plates which were welded together along seams transverse to the tubes but parallel to the common axial plane of each tube array. The transition or leveling flanges were provided to accommodate the outer boundaries of the tube bundle to the flanges of the housing which were bolted to the casing sandwiched between them. The flanges of the housing were provided with inlet and outlet hoods for the introduction of the hot gas to be cooled and for the affluent gases, respectively.

Because of the seams connecting the outwardly flared edges to narrow ends of the adjacent tube arrays, only the tubes defined between each pair of plates communicated with the hoods; the latter consequently formed manifolds at the opposite longitudinal ends of the tube bundle. The coolant passed through the bundle in spaces between the tube arrays enclosed by the seamed outwardly-turned or flared edges. The edge portions of the plates which formed the tubes were affixed to the housing wall transversely of the direction in which the tubes extended and laterally of the manifold ends of the assembly. The edge portions were relatively wide to space the tubes closest to the housing wall at a substantial distance therefrom which is greater than the spacing between the tubes to permit the trouble-free development of a temperature gradient corresponding to the temperature difference between the tube and the coolant or the coolant-enclosure housing. The welded seams at which the tube bundle was fixed to the housing flanges were therefore destressed and the thermal stresses resulting from temperature differences were taken up by the relatively wide sheet metal strips along the respective plates. The tube bundle of application Ser. No. 773,082 thereby eliminated the need for tube sheets at the opposite ends of the heat exchanger since the closure of the coolant chamber was accomplished by the ends of the same plates which produced the tubes. The tubes and end walls had practically the same wall thickness, thereby eliminating temperature differential stresses between tubes and tube sheets. The outwardly graded (transition) edges of the plate at both ends of the tube bundle had reinforcing webs or ribs set inwardly from the seams by which the edges were joined to the housing and ran transversely to the tube plates but parallel to the aforementioned outer edges, thereby stiffening the latter. Best results were described as being obtained when the curvature of the corrugations was circular so that the corrugations were effectively semicylindrical.

The housing structure was designed such that the inlet for the cooling liquid was located at the bottom of the unit while the outlet means extended upwardly therefrom and communicated above the housing with a separate chamber in which the condensate is precipitated. The chamber was connected by a conduit with one or both of the inlet fittings in a return path for the accumulated liquid at the lower side of the housing. There was provided a plurality of inlet fittings for the liquid coolant which could be connected separately or collectively to the precipitating drum.

OBJECTS OF THE INVENTION It is the principal object of the present invention to provide an improved heat exchanger which extends principles originally set forth in the aforementioned commonly assigned copending application.

Another object of the invention is to provide a lowcost efficient heat exchanger of relatively simple construction and of particular suitability for use in cryogenic processes.

It is, further, an object of the invention to provide an improved heat exchanger adapted to be used as a reflux boiler, condenser-evaporator, or head condenser in a single or double air-rectification column, of the Linde- Frankl type.

BRIEF STATEMENT OF THE INVENTION These objects and others which will become apparent hereinafter, are attained in accordance with the present invention, through the provision of a heat exchanger which basically comprises a cylindrical cas ing having a vertical axis and a prismatic heat-exchange body having at least four surfaces lying along chords of the cylinder and defining chambers and ducts therewith which communicate with the body of the heatexchanger unit. This prismatic assembly consists, in accordance with the principles of the earlier application, of a plurality of parallel arrays of parallel passages, each array of passages being defined between a pair of plates formed with confronting semicylindrical cavities which register to provide tubes of arcuate section. The spaces between the pairs of plates and the tube arrays define inner compartments, according to the present invention, which are closed at top and bottom, by outwardly flared flanges or marginal portions of the plates defining each tube array and butt-welded together along horizontal seams. The segmental chambers defined between opposite flat sides of the prismatic body and the cylindrical housing communicate laterally with the intermediate compartments.

. those set forth in the aforementioned According to a more specific feature of this invention, at least one pair of cylinder-segmental compartments is defined by a pair of walls lying along chords of the cylinder and flank the prismatic body parallel to the plates thereof. Below the prismatic body, we provide a further wall constituting a chamber opening upwardly and into the interior of the tubes or passages of the array and communicating with cylinder-segmental ducts defined by the plates. For the purposes of the present invention, the prismatic body must have at least four lateral sides although a larger number of sides is not excluded, it being preferred that there be an even number of lateral sides, i.e. four, six, eight, etc.

In a particularly desirable configuration of the heat exchangerot the present invention, the prismatic body constitutes part of a condenser-evaporator for use in a double column of the Linde-Fraenkle air-rectification type, as a head condenser in an air-rectification column or as a reflux boiler in the sump of such a column and is built directly in the cylindrical column which here forms the case. The advantage of this construction is that the plate stack allows, for any fluid capacity, a relatively small height and eliminates the need for expansion of the column. The low-pressure medium may traverse the round-section passages (concave passages) while the high-pressure medium traverses the intermediate compartments so that stress upon the stack and upon the plates is distributed and used to stabilize the assembly. These principles are, of course, similar to copending application. 1

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a horizontal crosssection through an airrectification condenser-evaporator according to the present invention, taken generally along the line I I of FIGS. 2 and 3;

FIG. 2 is a vertical cross-section taken along the line II II ofFIG. 1;

FIG. 3 is a vertical cross-section taken at right angles to the cross-section of FIG. 2 and along the line III III of FIG. 1;

FIGS. 4 6 are diagrams representing various configurations of the profiled plates used in the air-rectification installation of the present invention; and

FIG. 7 is a sectional view through the system of FIG. 6, illustrating additional features of the invention.

SPECIFIC DESCRIPTION In the following description, reference is made to a condenser-evaporator for an air-rectification installation, by way of example. In such a device, air is separated into its components by liquefaction and fractional vaporization, the coolant being a liquefied or gaseous rectification product, eg nitrogen or oxygen. A gas is thereby cooled to form a condensate which can be collected and vaporized elsewhere in the system if the desire is to obtain the pure or relatively pure gas. Alternatively, the condensate can be retained in a liquid state. A liquid rectification product may be introduced such a heat exchanger and vaporized therein while cooling the relatively warmer fluid. A typical airrectification installation using condenser-evaporators, head condensers and reflex boilers of the type described may be found in PERRYS CHEMICAL EN- GINEERS HANDBOOK, McGraw Hill Book Comp., New York, Fourth Edition, pages 12 28 ff. (1963). In general, the condenser evaporator or condenser-boiler is incorporated in a rectification column which is of cylindrical configuration. However, the heat exchanger of the present invention may be used as an evaporatorcondenser in other industrial processes and reference to an air rectification installation is not to be considered limiting in this respect, but only to identify the preferred utility.

In FIGS. 1 3 of the drawing, we show a cylindrical rectification column provided at 1 with a condenserevaporator or condenser-boiler heat exchanger in accordance with the present invention. In the direction of the vertical tower axis, there are provided flow passages 2 of the circular or round cross-section type which may hereinafter be described as tubes, the passages 2 being arrayed in parallel rows with respective axes defining planes parallel to the planes of the other arrays of passages and parallel to the vertical axis of the tower. As is best seen from FIG. 1, the passages 2 are transversely spaced by a distance D which is slightly less than 2r, r constituting the radius of the passage or tube. In addition, the tubes 20 and 2b of a pair of adjacent or neighboring arrays are transversely offset or staggered by a distance S equal approximately to D/2 or half the distance between the tubes measured center to center. The construction of such arrays of passages is fully described in the commonly assigned copending application mentioned earlier.

As specified in the latter application, the passages 2 of each planar array are formed by joining two semitube-profile (corrugated) plates or sheets 3 and 4, again best seen in FIG. 1. As illustrated, the plate 3 is provided with semicylindrical concavities 3a, spaced apart by flat rectangular webs 3b and registering with similar concavities 4a deformed in the plate 4 and spaced by webs 4b. The webs between the semicylindrical concavities likewise are juxtaposed and, when the plates are sealed in face-to-face relationship with their semicylindrical concavities in registering relationship, they define the tubes 2. The profile plates 3 and 4 are formed along their edges lying perpendicular to the axis of the housing with slightly rounded horizontally extending sections 5 and 6 which are joined together along butt-welded seams 7 whereby compartments are defined between the adjacent tube arrays as represented, for example, at 19. In addition, each pair of plates is welded together along the edges 8 parallel to the axis of the column.

To supply the vaporizable oxygen to the passages 2 of the condenser-evaporator of FIGS. 1 3 at the bottom openings 9 of these passages, we provide a pair of partitions or walls, 10, 11 which extend parallel to the plates 3 and 4 (FIGS. 1 and 2). The plates 10 and 11 define with the cylindrical housing wall 1 cylindrical segments 12 and 13, corresponding to sections lying along chords of the cylinder 1 and which communicate with a space 9a (FIG. 2) below the openings 9 as indicated at 31. The bottom of the space 9a is defined by an upwardly convex floor 14 which is generally horizontal and is centered upon the axis of the cylinder, while having planar end portions 14a welded to the inner wall of the cylinder beneath the ducts 12 and 13. At right angles to the ducts 13, the marginal portions of the floor 14 curve upwardly as represented at 14b to define a manifold registering with the array of bottom openings 9. At their bottom ends, therefore, the ducts l2 and 13 can communicate only with the space 9a and only with the passages 2 at the bottom thereof.

Additional walls may be provided to form, between the cylinder-segmental ducts 12 and 13, a pair of further cylindrical segmental chambers 17 and 18 laterally communicating with the spaces 19 intermediate the tube arrays 2 formed between each pair of tube plates 3, 4. The intermediate spaces 19 can, as shown in the drawing, be fully open into the chambers 17 and 18. A simple construction is provided when the edges of the plates 3 and 4 confronting the chambers 17 and 18 lie along common planar surfaces 20 (FIGS. 1 and 3), the surfaces 20 extending along chords of the cylinder 1 and defining the segmental chambers 17 and 18. In the ambodiment illustrated in FIGS. 1 3, the array of tube plates is prismatic and has eight lateral sides, i.e. is octagonal so that a pair of opposite sides are provided with the plates and 11, previously described, while three sides of the octagon define the space 17 and the other three sides limit the space 18 as illustrated in FIG. 1. The chambers 17 and 18 are closed at their upper ends by inclined partitions 21 and 22 (FIG. 3) while they remain open downwardly in regions unobstructed by the bottom wall 14. At the upper ends, the chambers 17 and 18 communicate with radial outlet ducts 23 and 24 (FIG. 3) which connect with the chambers through the wall of the cylindrical housing 1 within the space bounded by the inclined plates 21 and 22.

The upper region 25 of the intermediate compartments 19, i.e. the cimpartments between the tube arrays, is separated from the lower section of these compartments by horizontal partitions 28 (FIGS. 1 and 3), the partions being open at the center to provide windows 28' (FIGS. 1 and 3). The partitions 28 also run through the cylinder'segmental chambers 17 and 18 to separate the upper regions 26 and 27 thereof from the lower regions therebeneath (FIG. 3). The partitions 28 in the intermediate compartments 19 may be of corrugated configuration parallel to the axes of the passages 2 and corresponding to the corrugations defining the chambers 19 whereby a tight fit about the corrugations is provided. Reference is made, at this point, to the plate 128 of FIG. 7 which is formed with semicircular cutouts 128' closely fitting about the convex semicylindrical portion 103a of tube plate 103 which, together with tube plate 104 defines the cylindrical passage 102. Here the partition 128 also has corrugations complementary to those of the intermediate space 19, 119 and fits about the plates 3, 4 and 103, 104 sealingly. Instead the plate l28b may be smooth-edged and engage in creases (128a) in the plates.

The device of FIGS. 1 3 may be employed in a rectification, as a condenser-evaporator in the following manner. The condenser-evaporator is incorporated in an air-rectification column (see the Handbook of Chemical Engineering cited earlier) having a multiplicity of stages in the column portion above the condenser-evaporator, the lowest stage or bottom 30 being illustrated in FIG. 2. The liquid oxygen collected on the bottom 30 passes, as represented by arrow 31, through the cylinder-segmental ducts l2 and 13 to the lower inlets 9 of the passages or tubes 2 (see FIG. 2). To this end, the rectification column above the condenserevaporator may have the usual perforated plate or hellcap plate 30a and is formed with a weir 30b defining the thickness of the liquid layer 300 of oxygen thereon. Gases rising through the perforated plate, therefore, bubble through this liquid layer in accordance with airrectification principles. The accumulation of liquid on the perforated plate 30a leads to overflow at the weirs which are provided with vapor-excluding traps 30d leading the overflow liquid into the ducts 12 and 13. The liquid oxygen passes upwardly through the tubes 2 as best seen on FIGS. 2 and 3 and as represented by the arrows 31.

In traversing the tubes 2, the liquid oxygen is evaporated in part by heat absorption through the walls of the tubes from the fluid traversing the chambers 19 so that the vapors pass upwardly from the tubes 2 (arrows 32) and traverse the bottom 30 of the rectification column.

Gaseous nitrogen is fed, as represented by arrows 32, from the underlying portion of the rectification column (FIG. 3) to the cylindrical segmental chambers 17 and 18 and thence through the compartments 19 between the tube plates 3 and 4 laterally. The'nitrogen, by heat transfer through the walls of the tubes 2, is liquefied (condensed) as a film on the surfaces of the plates 3 and 4 bounding the compartments l9 and externally of the tubes 2, the condensate passing downwardly along the walls (arrows 34) and being collected in the horizontal sections 5 and 6 whereby the condensste is led downwardly (arrow 34 in FIG. 3) to the overlying portion of the rectification column along the sides thereof.

The noncondensed helium which was introduced together with the nitrogen, passes through the windows 28a, 35 formed in the partitions 28 into the upper section of the compartment 19 and the upper sections 26, 27 of cylinder-segment chambers 17 and 18 and are led from the apparatus through the outlets 23 and 24. The helium flow path is represented by the arrows 36.

In FIGS. 4 6 and 7, we have shown, in diagrammatic form, configurations of condensate-film breakers as are provided on the walls of the compartments 19, i.e. on the outer surfaces of the tube plates 3 and 4. In the system of FIG. 4, the condensate film is broken by vertical ribs 37 which are disposed in parallel relationship along a plurality of vertically spaced rows, the rows being inclined downwardly from one side of the plate to the other. Such arrays may be spaced along the walls of compartment 19 or may extend over the entire wall, the corrugations being unillustrated in this Figure and FIGS. 5 and 6. The vertical ribs 37 are of limited height and length and cooperate with inclined condensate-collecting ribs 38 which extend along each array of vertical ribs 37. The condensate-collecting ribs 38 are of greater height than the ribs 37 and we have found, in practice, that the vertical ribs 37 should have a height of 0.5 to 0.7 mm while the ribs 38 should have a height of about 1 mm.

All of the condensate-collecting ribs 38 are parallel and of the same inclination (about 20 to the horizontal) and, in the region of the edge of the plate, terminate to define a downwardlyextending condensate channel 39 which leads to the floor of the intermediate chambers 19.

In FIG. 5, we have shown another construction of the film-breaking ribs and in this embodiment, the vertical ribs 37 extend in inverted-V arrays and co-operate with condensate-collecting ribs 40 and 41 which extend symmetrically upwardly to a vertex 42 lying approximately at the center of the plate. The downwardly inclined condensate-collecting ribs terminate short of a pair of downwardly extending channels formed along the opposite vertical sides of the ribs. Since the condennicating with at least one of said chambers and said sate is required in the system of FIG. to travel a shorter path, it is led from the plate more rap'idly'and the heat transfer to the condensation side is improved.

With the type of plate illustrated in FIG. 6, the condensate-collecting ribs 45, 46 extend along zigzag patterns or undulations while the vertical ribs 37 are of greater or lesser length, depending upon the pattern. The sections 45 and 46 of the condensate-collecting ribs extend respectively upwardly and downwardly, when considered from one side of the plate to the other and are of equal length to form vertices as described in connection with FIG. 5 as well as nodes at which traversely extending dropping projections 47 are provided (see also FIG. 7). The dropping projections 47, 47 of the tube walls flanking the intermediate compartment 19 or 119 reach approximately to the center of the intermediate compartment and are there provided with a condensate-runoff foil 50 of synthetic resin, the foil being perforated at 51. The foil 50 has the same area as the projection of the condensation surface. The condensate is found with the system of FIGS. 6 and 7 to reach the bottom of the tube array most rapidly, and is conducted most rapidly from the heatexchange surfaces so that optimal efficiency is provided.

From FIG. 7, it is also apparent that the vertical ribs 37 and the condensate-collecting ribs 46' can be formed in the plates 3, 4 by pressing, embossment or the like, as shown for the plate 104. Alternatively, the formations 37, 46, 47 may be provided as sheet-metal units which are secured, as to the plate 103, by immersion or sweat-soldering. It is also apparent that the inner surface of the tubes 2 can be provided with heatexchange-promoting formations (see plate 104) in a similar manner.

The improvement described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spiritand scope of the invention except as limited by the appended claims.

We claim:

1. A gas-rectification double column having a cylindrical housing and operating with a low pressure fluid and a high pressure fluid, a prismatic heat-exchanger body received in said housing and having at least four generally planar sides defining with said housing corresponding cylinder-segmental chambers, said body being composed of a stack of tube arrays, each of said arrays being formed by a pair of juxtaposed plates formed with arcuate confronting semicylindrical concompartments communicating with at least another of said chambers, and means for passing heat-exchange fluids through said one and said other chamber and including a bottom wall defining a space below said body communicating with said tubes from below and with said one of said chambers, said compartments opening laterally directly into said other of said chambers, said lowpressure fluid being conducted through said tubes high-pressure side but enables heat exchange between said low-pressure side and the high-pressure side of said column.

2.- The gas-rectification column heat exchanger defined in claim 1 wherein said body has a pair of opposite lateral sides generally parallel to said plates, said means for passing said heat-exchange fluids through said one chamber including a pair of partitions flanking said stack along said opposite lateral sides and parallel to said plates while defining a pair of cylinder-segmental duets with said housing, said ducts communicating with said space below said body.

3. The gas-rectification column heat exchanger defined in claim 1 wherein said body is provided with generally planar sides at which said compartments open and defining with said housing a pair of chambers communicating with said compartments over substantially all of said opposite sides.

4. The gas-rectification column heat exchanger defined in claim 3 wherein said tubes and said pair of chambers open upwardly, said means for passing said heat-exchange fluids through said other chamber including walls defining discharge compartments at the upper ends of said pair of chambers and outlets extending through the wall of said housing for discharging fluids collected in said outlet chambers.

5. The gas-rectification column heat exchanger defined in claim 4, further comprising partition means extending through said compartments toward the upper ends thereof for subdividing said compartments into upper and lower sections, said partition means being interrupted at a central location.

6. The gas-rectification column heat exchanger defined in claim 5 wherein said partition means cylindrically engage the plates defining said intermediate compartments.

7. The gas-rectification column heat exchanger defined in claim 6 wherein the surfaces of said intermediate compartments are formed with arrays of vertically extending condensate-film-breaking ribs and downwardly inclined condensate-collecting ribs.

8. The gas-rectification column heat exchanger defined in claim 7 wherein said condensate-collecting ribs of each surface of each intermediate compartment extend downwardly and outwardly with the same inclination, said plates being formed along at least one lateral edge with a downwardly extending condensatecollecting channel, said condensate-collecting ribs terminating in said channel.

9. The gas-rectification column heat exchanger defined in claim 8 wherein the condensate-collecting ribs of each surface of each intermediate compartment extend symetrically downwardly and outwardly from respective vertices to condensate-collecting channels on opposite sides of each plate.

10. The gas-rectification column heat exchanger defined in claim 7 wherein said condensate-collecting ribs form notes, said surfaces of said intermediate chambers being formed with drop-forming projections extending transversely from said notes toward the center in respective compartments for leading conden- 

1. A gas-rectification double column having a cylindrical housing and operating with a low pressure fluid and a high pressure fluid, a prismatic heat-exchanger body received in said housing and having at least four generally planar sides defining with said housing corresponding cylinder-segmental chambers, said body being composed of a stack of tube arrays, each of said arrays being formed by a pair of juxtaposed plates formed with arcuate confronting semicylindrical concavities defining parallel passages in the form of cylindrical tubes between each pair of plates, said tubes extending parallel to the axis of the cylindrical housing, the edges of the plates being secured to the edges of the plates of adjacent arrays to define intermediate compartments between said arrays, said passages communicating with at least one of said chambers and said compartments communicating with at least another of said chambers, and means For passing heat-exchange fluids through said one and said other chamber and including a bottom wall defining a space below said body communicating with said tubes from below and with said one of said chambers, said compartments opening laterally directly into said other of said chambers, said low pressure fluid being conducted through said tubes and said high pressure fluid being passed through said compartments, said column having a low-pressure side communicating with said one of said chambers and a high-pressure side communicating with said compartments through said other chamber whereby said body physically separates said low-pressure side from said high-pressure side but enables heat exchange between said low-pressure side and the high-pressure side of said column.
 2. The gas-rectification column heat exchanger defined in claim 1 wherein said body has a pair of opposite lateral sides generally parallel to said plates, said means for passing said heat-exchange fluids through said one chamber including a pair of partitions flanking said stack along said opposite lateral sides and parallel to said plates while defining a pair of cylinder-segmental ducts with said housing, said ducts communicating with said space below said body.
 3. The gas-rectification column heat exchanger defined in claim 1 wherein said body is provided with generally planar sides at which said compartments open and defining with said housing a pair of chambers communicating with said compartments over substantially all of said opposite sides.
 4. The gas-rectification column heat exchanger defined in claim 3 wherein said tubes and said pair of chambers open upwardly, said means for passing said heat-exchange fluids through said other chamber including walls defining discharge compartments at the upper ends of said pair of chambers and outlets extending through the wall of said housing for discharging fluids collected in said outlet chambers.
 5. The gas-rectification column heat exchanger defined in claim 4, further comprising partition means extending through said compartments toward the upper ends thereof for subdividing said compartments into upper and lower sections, said partition means being interrupted at a central location.
 6. The gas-rectification column heat exchanger defined in claim 5 wherein said partition means cylindrically engage the plates defining said intermediate compartments.
 7. The gas-rectification column heat exchanger defined in claim 6 wherein the surfaces of said intermediate compartments are formed with arrays of vertically extending condensate-film-breaking ribs and downwardly inclined condensate-collecting ribs.
 8. The gas-rectification column heat exchanger defined in claim 7 wherein said condensate-collecting ribs of each surface of each intermediate compartment extend downwardly and outwardly with the same inclination, said plates being formed along at least one lateral edge with a downwardly extending condensate-collecting channel, said condensate-collecting ribs terminating in said channel.
 9. The gas-rectification column heat exchanger defined in claim 8 wherein the condensate-collecting ribs of each surface of each intermediate compartment extend symetrically downwardly and outwardly from respective vertices to condensate-collecting channels on opposite sides of each plate.
 10. The gas-rectification column heat exchanger defined in claim 7 wherein said condensate-collecting ribs form notes, said surfaces of said intermediate chambers being formed with drop-forming projections extending transversely from said notes toward the center in respective compartments for leading condensate away from said condensate-collecting ribs.
 11. The gas-rectification column heat exchanger defined in claim 10, further comprising a synthetic-resin foil extending through each of said intermediate compartments and cooperating with said projections for conducting condensate to the bottoms of the respective compartment.
 12. The gas-rectification column heat eXchanger defined in claim 11 wherein said foil is perforated.
 13. The gas-rectification column heat exchanger defined in claim 7 wherein said ribs are embossed in said plates. 